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Bearing steel quality requirements and shortcomings (3)
Source: Bearing network time: 2018-07-09
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(3) Non-metallic inclusions: steel in the process of exercise and casting; chemical reaction products and deoxidation products caused by the contact between the molten steel and the molten steel and the lining; and the furnace wall and the steel tapping tank , steel ladle; soup and other anti-inflammatory materials are eroded and fall into the molten steel. These non-steel liquid materials that enter the molten steel and are not discharged are called non-metallic impurities. The presence of non-metallic inclusions in the bearing steel; One of the main reasons for the service life of steel. Non-metallic inclusions in steel are classified into the following types according to their characteristics, shape and dispersion.
Oxide: It is more brittle; it is also called brittle noisy; it is usually distributed in a chain in the rolling direction; such as aluminum oxide (Al2O3) and iron oxide (FeO).
Sulfide: has good plasticity; can be deformed; it is also called plastic noisy. It is distributed in the steel in the rolling direction. For example, iron sulfide (FeS) and manganese sulfide (MnS) belong to this category. Outside the material; silicate also has a certain plasticity; also known as plastic inclusions.
Point-like non-deformed inclusions: brittle and hard; in the steel, point or spherical; not deformed during processing; such as quartz (SiO2), aluminosilicate (3Al2O3, 2SiO2) and calcium silicate .
(4), carbide non-uniformity: high carbon bearing steel carbon is high; and is enriched with a certain amount of carbide constituent elements (such as chromium). In the process of steel liquid condensation; these elements are prone to segregation of components; Lead to unevenness in the dispersion of carbides in steel.
Carbide liquid precipitation: molten steel in the crystallization process; because the cooling rate is too slow; constitutes a severe segregation of carbon components. It forms a coarse primary carbide between the dendrites; this primary carbide is difficult to eliminate. The direction of the strip is the same as that of the non-metallic inclusions; therefore, there is severe control in the technical standards of steel.
Carbide ribbon: its constituents are the same as carbide liquid precipitation. The coarse primary carbides that are broken during the casting and rolling process are gathered in small pieces and form a strip-like dispersion along the rolling direction. Carbide ribbon Severe will affect the heat treatment quality of the parts; make the parts of the parts less hot or overheated; the hardness of the parts is not uniform; the arrangement is uneven. The quality of the heat treatment of the parts is unqualified. When the carbide strips and carbides are severely analyzed; Bearing parts are fatigued early.
Carbide mesh: steel in the process of casting and rolling cooling; the solubility of austenite to carbon decreases with temperature. If the cooling rate is too slow between 800 and 900 °C, carbon is separated from austenite. And disperse the grain boundary; form a secondary carbide between the grain boundaries; exist in the form of a network; so it is called a carbide network. The carbide is a hard and brittle phase; the connectivity between the grains is damaged; The impact toughness of the steel is reduced. Thus; the life of the bearing parts is reduced.
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